1,528 research outputs found
Gamma rays from muons from WIMPs: Implementation of radiative muon decays for dark matter analyses
Dark matter searches in gamma ray final states often make use of the fact
that photons can be produced from final state muons. Modern Monte Carlo
generators and DM codes include the effects of final state radiation from muons
produced in the dark matter annihilation process itself, but neglect the O(1%)
radiative correction that arises from the subsequent muon decay. After
implementing this correction we demonstrate the effect that it can have on dark
matter phenomenology by considering the case of dark matter annihilation to
four muons via scalar mediator production. We first show that the AMS-02
positron excess can no longer easily be made consistent with this final state
once the Fermi-LAT dwarf limits are calculated with the inclusion of radiative
muon decays, and we next show that the Fermi-LAT galactic centre gamma excess
can be improved with this final state after inclusion of the same effect. We
provide code and tables for the implementation of this effect in the popular
dark matter code micrOMEGAs, providing a solution for any model producing final
state muons.Comment: 11 pages, 7 figures + anc file
Fluid Interpretation of Cardassian Expansion
A fluid interpretation of Cardassian expansion is developed. Here, the
Friedmann equation takes the form where contains
only matter and radiation (no vacuum). The function g(\rhom) returns to the
usual 8\pi\rhom/(3 m_{pl}^2) during the early history of the universe, but
takes a different form that drives an accelerated expansion after a redshift . One possible interpretation of this function (and of the right hand
side of Einstein's equations) is that it describes a fluid with total energy
density \rho_{tot} = {3 m_{pl}^2 \over 8 \pi} g(\rhom) = \rhom + \rho_K
containing not only matter density (mass times number density) but also
interaction terms . These interaction terms give rise to an effective
negative pressure which drives cosmological acceleration. These interactions
may be due to interacting dark matter, e.g. with a fifth force between
particles . Such interactions may be intrinsically four
dimensional or may result from higher dimensional physics. A fully relativistic
fluid model is developed here, with conservation of energy, momentum, and
particle number. A modified Poisson's equation is derived. A study of
fluctuations in the early universe is presented, although a fully relativistic
treatment of the perturbations including gauge choice is as yet incomplete.Comment: 25 pages, 1 figure. Replaced with published version. Title changed in
journa
Are we seeing the beginnings of Inflation?
Phantom Cosmology provides an unique opportunity to "connect" the phantom
driven (low en- ergy meV scale) dark energy phase to the (high energy GUT
scale) inflationary era. This is possible because the energy density increases
in phantom cosmology. We present a concrete model where the energy density, but
not the scale factor, cycles through phases of standard radiation/matter domi-
nation followed by dark energy/inflationary phases, and the pattern repeating
itself. An interesting feature of the model is that once we include
interactions between the "phantom fluid" and ordinary matter, the Big rip
singularity is avoided with the phantom phase naturally giving way to a near
exponential inflationary expansion.Comment: 17 pages, 1 figur
Hybrid natural inflation from non Abelian discrete symmetry
A spontaneously broken global discrete symmetry may have pseudo Goldstone
modes associated with the spontaneous breaking of the approximate continuous
symmetry of the low dimension terms in the Lagrangian. These provide natural
candidates for an inflaton that can generate slow roll inflation. We show that,
in the case of a non Abelian discrete symmetry, the pseudo Goldstone modes
readily couple to further scalar fields in a manner that the end of inflation
is determined by these additional scalar fields, generating hybrid inflation.
We give a simple parameterisation of the inflationary potential in this case,
determine the inflationary parameters resulting, and show that phenomenological
successful inflation is possible while keeping the scale of symmetry breaking
sub-Plankian. Unlike natural inflation the inflation scale can be very low. We
construct two simple hybrid inflation models, one non supersymmetric and one
supersymmetric. In the latter case no parameters need be chosen anomalously
small.Comment: Accepted for publication in Phys. Lett.
Characterizing fully principal congruence representable distributive lattices
Motivated by a recent paper of G. Gr\"atzer, a finite distributive lattice
is said to be fully principal congruence representable if for every subset
of containing , , and the set of nonzero join-irreducible
elements of , there exists a finite lattice and an isomorphism from the
congruence lattice of onto such that corresponds to the set of
principal congruences of under this isomorphism. Based on earlier results
of G. Gr\"atzer, H. Lakser, and the present author, we prove that a finite
distributive lattice is fully principal congruence representable if and
only if it is planar and it has at most one join-reducible coatom. Furthermore,
even the automorphism group of can arbitrarily be stipulated in this case.
Also, we generalize a recent result of G. Gr\"atzer on principal congruence
representable subsets of a distributive lattice whose top element is
join-irreducible by proving that the automorphism group of the lattice we
construct can be arbitrary.Comment: 20 pages, 8 figure
Protogalactic Extension of the Parker Bound
We extend the Parker bound on the galactic flux of magnetic
monopoles. By requiring that a small initial seed field must survive the
collapse of the protogalaxy, before any regenerative dynamo effects become
significant, we develop a stronger bound. The survival and continued growth of
an initial galactic seed field G demand that . For a given
monopole mass, this bound is four and a half orders of magnitude more stringent
than the previous `extended Parker bound', but is more speculative as it
depends on assumptions about the behavior of magnetic fields during
protogalactic collapse. For monopoles which do not overclose the Universe
(), the maximum flux allowed is now cm^{-2}
s^{-1} sr^{-1}, a factor of 150 lower than the maximum flux allowed by the
extended Parker bound.Comment: 9 pages, 1 eps figur
Holes in the walls: primordial black holes as a solution to the cosmological domain wall problem
We propose a scenario in which the cosmological domain wall and monopole
problems are solved without any fine tuning of the initial conditions or
parameters in the Lagrangian of an underlying filed theory. In this scenario
domain walls sweep out (unwind) the monopoles from the early universe, then the
fast primordial black holes perforate the domain walls, change their topology
and destroy them. We find further that the (old vacuum) energy density released
from the domain walls could alleviate but not solve the cosmological flatness
problem.Comment: References added; Published in Phys. Rev.
A revision of the Generalized Uncertainty Principle
The Generalized Uncertainty Principle arises from the Heisenberg Uncertainty
Principle when gravity is taken into account, so the leading order correction
to the standard formula is expected to be proportional to the gravitational
constant . On the other hand, the emerging picture suggests a
set of departures from the standard theory which demand a revision of all the
arguments used to deduce heuristically the new rule. In particular, one can now
argue that the leading order correction to the Heisenberg Uncertainty Principle
is proportional to the first power of the Planck length . If so, the
departures from ordinary quantum mechanics would be much less suppressed than
what is commonly thought.Comment: 6 pages, 1 figur
Hybrid Natural Low Scale Inflation
We discuss the phenomenological implications of hybrid natural inflation
models in which the inflaton is a pseudo-Goldstone boson but inflation is
terminated by a second scalar field. A feature of the scheme is that the scale
of breaking of the Goldstone symmetry can be lower than the Planck scale and so
gravitational corrections are under control. We show that, for supersymmetric
models, the scale of inflation can be chosen anywhere between the Lyth upper
bound and a value close to the electroweak breaking scale. Unlike previous
models of low scale inflation the observed density perturbations and spectral
index are readily obtained by the choice of the free parameters
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